acquiring string output when i hit enter when input is finished - c++

Question

#include <iostream> // to generate the hexadecimal representation of a number
#include<string>
using std::string;
int main()
{
const string hexdigits("0123456789ABCDEF"); //possible hexdigits
std::cout << "enter the series of numbers between 0 and 15"
<< "separated by space. Hit enter when finished: "
<< std::endl; //line to be printed on screen
string result; // it will hold hexadecimal representation of the number
string::size_type n; // undefined string variable will hold numbers
while (std::cin >> n) // input number with just spaces
{
if (n < hexdigits.size()) // compares n with hexdigits size
{
result += hexdigits[n]; // storing string output in result
}
}
std::cout << "your hex number is: " << result << std::endl; //output result
return 0;
}
when I press ENTER after input, the output hex is not automatically generated. I have to use escape sequence \n after input, to proceed to output. how can I get my output with just hitting ENTER after give input numbers?
I tried using getline to get the whole line and exit, as given below
while(std::getline(std::cin, n))
but it gave error E0304
no instance for overloaded function 'std::getline' matches the argument list".

Answer 1

You need to provide a std::string argument to getline. The conversion is not correct either in several ways, but there are a lot of examples that show how to convert a hex string to a number. For example:
#include <iostream>
#include <string>
#include "stdlib.h"
int main()
{
std::string line;
if (std::getline(std::cin, line))
{
unsigned int value = strtoul(line.c_str(), NULL, 16);
std::cout << "your hex number is: " << value << std::endl; //output result
}
return 0;
}

Answer 2

You're a bit confused about types and logic. Firstly while(std::getline(std::cin, n)) does not work because n is not a string, getline only works with strings. Secondly even if getline worked with numbers the logic would not be correct because you want to input a single line but a while loop with getline would input multiple lines.
The answer is to use getline once to input a single line and then use a while loop to convert each of the numbers in the single line. To do this you have to know how to read numbers from a string (instead of from the console). I guess this is the part you are missing.
Here's some sample code (untested)
#include <iostream>
#include <sstream>
#include <string>
int main()
{
const std::string hexdigits("0123456789ABCDEF"); //possible hexdigits
std::cout << "enter the series of numbers between 0 and 15"
<< "separated by space. Hit enter when finished: "
<< std::endl;
std::string line;
if (getline(std::cin, line)) // read a line
{
std::istringstream buf(line);
unsigned result = 0, n;
while (buf >> n) // read numbers from the line
{
if (n < hexdigits.size())
{
result += hexdigits[n];
}
}
std::cout << "your hex number is: " << result << std::endl;
}
return 0;
}
BTW try to avoid commenting the obvious, comments like // compares n with hexdigits size add nothing to your code.